The Spacecraft Interaction Plasma Software package (SPIS), a three-dimension particle in cell (PIC) code, was used to model the Parker Solar Probe (PSP) spacecraft and FIELDS instrument and their interactions with the Solar wind. Our SPIS modeling relied on material properties of new spacecraft materials that we had obtained in previous work. The model was used to find the floating potentials of the spacecraft and FIELDS antennas at different distances from the Sun (from 1AU to 0.046AU). We find the following results: At greater distances from the Sun, the shadowed spacecraft charges negatively while the illuminated Thermal Protection System (TPS) charges positive due to the high resistance of the TPS Alumina shield at low temperatures. As the spacecraft approaches the Sun, the temperature of the TPS increases, the resistance between it and the spacecraft drops, and its photoemission increases, driving the spacecraft more positive. At the same time, an electrostatic barrier forms near the illuminated surface of the TPS and reflects the photoelectrons back leading to negative charging of some surfaces. The FIELDS antennas and shield also see this barrier forming but on a smaller scale. The FIELDS antennas charge positively at all distances modeled when no current bias is applied. Current biasing of the antennas affects their floating potential.

This research shows Part II of the Spacecraft Interaction Plasma Software (SPIS) used to model the Parker Solar Probe (PSP) FIELDS instrument and its interactions with the Solar Wind. Flight data was used to run the PSP model and compared with models using past predicted parameters. The effect of voltage biasing between the antenna, its shield, and the spacecraft on the current balance of each surface was investigated at first perihelion (0.16AU). The model data was reduced to I-V curves to find current saturations (analysis results 52µA versus flight results 54-72 µA), and sheath resistances (analysis results of 307 kΩ versus flight results of 51 kΩ). The recommended bias current to ensure optimal sensitivity of the FIELDS antenna was between -52 µA and -22 µA, which corresponded to a differential potential with respect to the spacecraft between -5V and 5V. The analysis also shows that plasma sheath of the FIELDS antenna and the plasma sheath of the FIELDS shield interacted between each other with an impedance of ~220kΩ.

Depressions in magnetic field strength, commonly referred to as magnetic holes, are observed ubiquitously in space plasmas. Sub-proton-scale magnetic holes with spatial scales smaller than or on the order of $\rho_p$, are likely supported by electron currents vortices, rotating perpendicular to the ambient magnetic field. While there are numerous accounts of sub-proton-scale magnetic holes within the Earth’s magnetosphere, there are no reported observations in other space plasma environments. We present the first evidence of sub-proton-scale magnetic holes in the Venusian magnetosheath. During Parker Solar Probe’s first Venus Gravity Assist, the spacecraft crossed the planet’s bow shock and subsequently observed the Venusian magnetosheath. The FIELDS instrument suite onboard the spacecraft achieved magnetic and electric field measurements of magnetic hole structures. The electric field associated with magnetic depressions are consistent with electron current vortices with amplitudes on the order of 1 $\mu$A/m$^2$.

We report observations of reconnection exhausts and associated ion and electron separatrix layers in and around the Heliospheric Current Sheet (HCS) during PSP Encounters 08 and 07, at 16 Rs and 20 Rs. HCS reconnection accelerated protons to almost twice the solar wind speed and increased the proton core energy by a factor of ~3, due to the Alfvén speed being comparable to the solar wind flow speed at these near-Sun distances. During E08, accelerated protons were found to have leaked out of the exhaust along separatrix field lines, appearing as field-aligned energetic proton beams in a broad region outside the HCS. Concurrent dropouts of strahl electrons, indicating disconnection from the Sun, provide further evidence for the HCS being the source of the beams. Around the HCS in E07, there were also proton beams but without electron strahl dropouts, indicating that their origin was non-local and closer to the Sun.

Quasi-Thermal Noise (QTN) spectroscopy is a reliable diagnostic routinely used for measuring electron density and temperature in space plasmas. The observed spectrum depends on both antenna geometry and plasma kinetic properties. Parker Solar Probe (PSP), launched in 2018, is equipped with an antenna system consisting of two linear dipoles with a significant gap between the antenna arms. Such a configuration, not utilized on previous missions, cannot be completely described by current models of the antenna response function. In this work, we calculate the current distribution and the corresponding response function for the PSP antenna geometry, and use these results to generate synthetic QTN spectra. Applying this model to the Encounter 7 observations from PSP provides accurate estimations of electron density and temperature, which are in very good agreement with particle analyzer measurements.